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Equipment Discussions >> Reflectors

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FirstSight
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Reged: 12/26/05

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Re: New Perspectives on Newtonian Collimation new [Re: Mike Harvey]
      #5674722 - 02/11/13 08:04 PM

I agree completely that collimation is much easier to understand by show-me than by read-me.

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starman345
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Reged: 07/06/10

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Re: New Perspectives on Newtonian Collimation new [Re: Mike Harvey]
      #5675263 - 02/12/13 04:53 AM

Quote:

Maybe one day Vic will produce a VIDEO companion to "New Perspectives".




+1
Got my New Perspectives copy a few days ago, well spent money, thanks Vic


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backwoody
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Reged: 01/08/07

Loc: Idaho USA
Re: New Perspectives on Newtonian Collimation new [Re: Vic Menard]
      #5676915 - 02/13/13 01:09 AM

Yeah Vic, Jim, Jason, Don...you guys taught many of us. Nice to acknowledge your expertise once in a while...

c/s always, and good collimation,


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Sarkikos
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Re: New Perspefctives on Newtonian Collimation new [Re: CatseyeMan]
      #5679301 - 02/14/13 12:00 PM

CatseyeMan,

Quote:

The trick here when using the autocollimator is to attach the clip light to the extreme side of the OTA opposite the focuser & aimed at the spot; when using the Cheshire, move the clip light in on the spider toward the center of the OTA adjacent to the Secondary pointing toward the spot.




Thanks for this tip. I've tried collimating in a dark room with a red light flashlight clipped to a spider vane but there was not enough light to see the donuts in my autocollimator. I probably didn't have it positioned as you advice. IMO, it's best to make trial runs at home of everything you can before you actually give it a try at the dark site.

I use an AstroSystems 1.25" autocollimator. I'll try your tip to see if it makes a difference for the AstroSystems model.

Mike


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precaud
Pooh-Bah
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Reged: 12/05/12

Loc: north central New Mexico
Re: New Perspefctives on Newtonian Collimation new [Re: Sarkikos]
      #5679326 - 02/14/13 12:12 PM

Mike, I just got the AstroSystems 1.25" autocollimator and what worked for me last night was a diffuse bright light shining toward the tube at an angle from out of the FOV. The object seems to be to flood the tube with indirect light. This was with the standard round paper donuts in my scopes, which I plan on changing out in the next week or so with more reflective ones, which should help.

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Sarkikos
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Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: New Perspefctives on Newtonian Collimation new [Re: Sarkikos]
      #5679370 - 02/14/13 12:32 PM

FWIW, personally I learn much better by reading and trying things out for myself than by having somebody show me how to do it. Just how I roll.

I just now ordered a copy of the book. I think I've been able to learn how to collimate very closely by reading threads here on CN - my avatar attests to that! - but it's nice to have all that knowledge condensed into one easy-to-access source. I'll undoubtedly pick up some more tips and refinements from the book.

Mike


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Sarkikos
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Re: New Perspefctives on Newtonian Collimation new [Re: precaud]
      #5679376 - 02/14/13 12:38 PM

Quote:

Mike, I just got the AstroSystems 1.25" autocollimator and what worked for me last night was a diffuse bright light shining toward the tube at an angle from out of the FOV. The object seems to be to flood the tube with indirect light. This was with the standard round paper donuts in my scopes, which I plan on changing out in the next week or so with more reflective ones, which should help.




Now, when I'm at my dark site at night I need to make sure that light is red and does not disturb other observers. So that will limit somewhat the brightness of the light and the location. I'd at least want to make sure that the light is inside the OTA, not sitting somewhere outside the telescope. I have a solid tube Dob, so if I attach the red light to a spider vane, that should be OK.

Using the autocollimator is easy during the day. IME, as long as the sun has not set for very long, the sky is still bright enough to stack the donuts.

Yes, I don't have a reflective triangle to mark the primary center, just a paper circle.

Mike


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precaud
Pooh-Bah
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Reged: 12/05/12

Loc: north central New Mexico
Re: New Perspefctives on Newtonian Collimation new [Re: Sarkikos]
      #5679475 - 02/14/13 01:27 PM

Yeah, the LED clipped inside the tube sounds like the way to go in those circumstances.

The AS AC came with a square reflective spot, just over 1/2" across. Seems like an odd choice of shape, not so easy to identify the inverted reflections as with a triangle.


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Starman1
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Reged: 06/24/03

Loc: Los Angeles
Re: New Perspefctives on Newtonian Collimation new [Re: precaud]
      #5679565 - 02/14/13 02:02 PM

Check the accuracy of the perpendicularity of the AC mirror by rotating the AC in the focuser and checking if the images unstack. If the images don't change, your mirror is fine.
It's wise to do this with any passive collimation tool just to be certain everything is nice and well-machined.


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Atl
professor emeritus
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Reged: 04/13/12

Re: New Perspefctives on Newtonian Collimation new [Re: Sarkikos]
      #5679574 - 02/14/13 02:06 PM

Quote:

Quote:

Mike, I just got the AstroSystems 1.25" autocollimator and what worked for me last night was a diffuse bright light shining toward the tube at an angle from out of the FOV. The object seems to be to flood the tube with indirect light. This was with the standard round paper donuts in my scopes, which I plan on changing out in the next week or so with more reflective ones, which should help.




Now, when I'm at my dark site at night I need to make sure that light is red and does not disturb other observers. So that will limit somewhat the brightness of the light and the location. I'd at least want to make sure that the light is inside the OTA, not sitting somewhere outside the telescope. I have a solid tube Dob, so if I attach the red light to a spider vane, that should be OK.

Using the autocollimator is easy during the day. IME, even if the sun has not set for very long, the sky is still bright enough to stack the donuts.

Yes, I don't have a reflective triangle to mark the primary center, just a paper circle.

Mike




Here is what I settled on. In daylight get the collimation right and use a laser once set up at night to touch up the collimation. It seems to work fine.


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Sarkikos
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Reged: 12/18/07

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Re: New Perspefctives on Newtonian Collimation new [Re: Atl]
      #5679595 - 02/14/13 02:17 PM

Quote:

Here is what I settled on. In daylight get the collimation right and use a laser once set up at night to touch up the collimation. It seems to work fine.




I think an autocollimator will produce a much closer collimation than a laser. I'd place the laser collimators at about the same level of accuracy as a Cheshire/sight-tube, and even then, only if the laser itself has been collimated.

What I do is collimate with my Cheshire/sight-tube and autocollimator at home either looking toward a light in the house or, even better, at the sky outside a window. Then I make sure to arrive at the dark site before sunset so I'll have enough light to check the collimation with my autocollimator. Usually the collimation is fine. Sometimes it just needs a slight tweak on the Bob's Knobs at the secondary to restack the donuts.

So far this has worked out OK, since I'd much rather set up my equipment in the daylight than in the dark with a red-light flashlight on my forehead. Of course, being able to collimate accurately in the dark would come in handy if I arrive late at the dark site.

Mike


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Sarkikos
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Re: New Perspefctives on Newtonian Collimation new [Re: Starman1]
      #5679607 - 02/14/13 02:22 PM

Don,

Quote:

Check the accuracy of the perpendicularity of the AC mirror by rotating the AC in the focuser and checking if the images unstack. If the images don't change, your mirror is fine.
It's wise to do this with any passive collimation tool just to be certain everything is nice and well-machined.




I've checked out my AstroSystems 1.25" AC in this way and it was right on.

Mike


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Jason D
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Re: New Perspefctives on Newtonian Collimation new [Re: Sarkikos]
      #5679652 - 02/14/13 02:43 PM

Quote:

I think an autocollimator will produce a much closer collimation than a laser. I'd place the laser collimators at about the same level of accuracy as a Cheshire/sight-tube, and even then, only if the laser itself has been collimated.




The quality of tools has a huge impact on the above statement. Autocollimators have much higher quality bar to get that extra accuarcy. Without that extra attention to quality, the autocollimator will not provide an additional accuracy -- might even making it worse.

Check the info in the following link
http://www.firstlightoptics.com/blog/how-to-choose-a-telescope-autocollimator...

Jason


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Jason D
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Re: New Perspefctives on Newtonian Collimation new [Re: Sarkikos]
      #5679661 - 02/14/13 02:45 PM

Quote:

I've checked out my AstroSystems 1.25" AC in this way and it was right on.




Make sure to do the test the proper way. Do not stack all reflections then rotate. Unstack a little to see all 4 reflections then rotate.

Jason


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Sarkikos
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Re: New Perspefctives on Newtonian Collimation new [Re: Jason D]
      #5679697 - 02/14/13 03:01 PM

Jason,

Quote:

Quote:

I think an autocollimator will produce a much closer collimation than a laser. I'd place the laser collimators at about the same level of accuracy as a Cheshire/sight-tube, and even then, only if the laser itself has been collimated.




The quality of tools has a huge impact on the above statement. Autocollimators have much higher quality bar to get that extra accuarcy. Without that extra attention to quality, the autocollimator will not provide an additional accuracy -- might even making it worse.




Well, if we were to compare a good quality autocollimator with a good quality laser collimator, which do you think would give a closer collimation?

I've gotten very good results with the AstroSystems autocollimator. I've never seen a laser collimator that was as accurate. But then again, I've never paid multiple hundreds for a laser collimator. On the other hand, IIRC the autocollimator only cost about $50.

Mike


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Jeff Morgan
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Reged: 09/28/03

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Re: New Perspectives on Newtonian Collimation new [Re: starman345]
      #5679722 - 02/14/13 03:15 PM

Quote:

Quote:

Maybe one day Vic will produce a VIDEO companion to "New Perspectives".




+1
Got my New Perspectives copy a few days ago, well spent money, thanks Vic




I've always been frustrated by getting good axial alignment and still having some skew in my diagonal holder. After Perspectives I finally saw how easy the solution was. And using the image of the shroud screw heads in the autocollimator was a definite "aha" moment - I never would have thought of it on my own.

I hope Vic gets an asteroid or something named after him for his contribution!


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: New Perspectives on Newtonian Collimation new [Re: Jeff Morgan]
      #5679791 - 02/14/13 03:57 PM

Alas, if using the "new Method" of collimation (Unidirectional Secondary Offset), the optical axis is tilted slightly toward the focuser and the angle of reflection at the secondary is greater than 90 degrees.
That's fine, because superb collimation can be achieved.
But, there are consequences:
1) The image of the secondary mirror will not be exactly round. It will appear ever-so-slightly shortened in the up tube/down tube direction. If you make the secondary mirror's reflective surface coincident with the inside edge of a sght tube, you will see this. It's tiny, but it's there.
2) The screws on the outside of the secondary shroud will not appear equally visible. That shroud will be slightly tipped relative to the optical centerline, making screws on the long edge of the shroud more visible than the screws on the short edge of the shroud. Admittedly, the effect is fairly small, but it's real, and it's visible. It's because the sides of the shroud are not in the same line as the optical axis.

To eliminate #1 and #2 above, classical offset (bi-directional secondary offset) needs to be employed. Then the sides of the secondary shroud will be parallel to the optical axis and the secondary will appear exactly round in outline in the sight tube.

And the larger the amount of offset, the greater the degree of #1 and #2 above as seen through collimation tools.

Again, it is not a great amount, and near-perfect collimation can be achieved. But the "New Model" (UDO) of collimation does have this issue.


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Atl
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Reged: 04/13/12

Re: New Perspectives on Newtonian Collimation new [Re: Jeff Morgan]
      #5679793 - 02/14/13 04:00 PM

I had the same issue. Putting paper behind the secondary showed me how messed up my secondary was... simple idea, but not obvious to me. I still have trouble with the autocollimator figuring out what knobs to turn to move those little triangles different ways, but it is happening.

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Jason D
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Re: New Perspefctives on Newtonian Collimation new [Re: Sarkikos]
      #5679813 - 02/14/13 04:15 PM

Quote:

Well, if we were to compare a good quality autocollimator with a good quality laser collimator, which do you think would give a closer collimation?



If you have a quality autocollimator and you apply it correctly starting with CDP using the single pupil autocollimator then yes it will be more accurate. Both quality and technique are required to get that extra accuracy with an autocollimator. Without the two, your collimation will be as good -- if not worse -- than a quality laser collimator.

Quote:

I've gotten very good results with the AstroSystems autocollimator. I've never seen a laser collimator that was as accurate. But then again, I've never paid multiple hundreds for a laser collimator. On the other hand, IIRC the autocollimator only cost about $50.



But if a lower quality $50 autocollimator does not give you any extra accuracy then it is a lesser value than a quality $100 one.
Refer to the autocollimator evaluation link I provided. If your $50 autocollimator pass the evaluation then you have a good collimator for a lower price.
I am not suggesting that you go off and spend a $100 on a quality autocollimator. That is your decision. Everyone is free to spend their money whichever way they want.

Jason


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precaud
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Reged: 12/05/12

Loc: north central New Mexico
Re: New Perspefctives on Newtonian Collimation new [Re: Jason D]
      #5679864 - 02/14/13 04:42 PM

That I'm aware of, the AS autocollimator is the only game in town for 1.25" . Please correct me if I'm wrong.

They are $45, or $35 when bought with the Lightpipe combo tool.

When checked at quadrant points, mine does not pass the rotation test, whether left loose or tightened on the focuser. The reflections' pattern moves cyclically with the tool's rotation. Leaving one with the question: which, if any, of these positions are correct?


Edited by precaud (02/14/13 05:22 PM)


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